A weld gun performs welding operations on metal workpieces. Generally, a weld gun has two electrodes. Workpieces to be welded together at weld locations are inserted between the pair of electrodes of the weld gun. Used herein, the term "workpiece" refers to at least two workpieces, or to portions of a single workpiece, to be welded together.
A robot arm cooperates with the weld gun for moving the weld gun relative to the workpiece. A robot controller controls the robot arm to move the weld gun to various weld locations of the workpiece. The weld controller controls the weld gun to close and move the electrodes toward the workpiece until the electrodes clamp down on the workpiece with a sufficient pressure such that the workpiece is inserted between the electrodes at a first weld location. The weld controller then controls a weld power supply to provide electrical power to the electrodes to effect welding at the weld location. The weld power supply then terminates the electrical power to the electrodes after the workpiece has been welded at the first weld location. The weld controller then controls the weld gun to open, release the pressure applied to the electrodes, and move the electrodes away from workpiece. The robot controller then controls the robot arm to move the weld gun from the first weld location to the second weld location.
Prior to the robot arm moving the weld gun to the second weld location, the electrodes have to be opened a sufficient distance to allow the workpiece to be inserted between the electrodes at the second weld location. If the electrodes are not opened the sufficient distance prior to being moved to the second weld location then the electrodes, the weld gun, the robot arm, and the workpiece may be damaged. After the electrodes have been opened to the sufficient distance the weld gun may be moved to the second weld location. The weld controller then controls the weld gun to close and move the electrodes toward the workpiece until the electrodes clamp down on the workpiece such that the workpiece is inserted between the electrodes at the second weld location. The above described process is then repeated to weld the workpiece at the second weld location.
The workpiece has a thickness at each weld location and a thickness between the weld locations. The thickness of the workpiece may be consistent or vary among the weld locations and between the weld locations. To clamp down on the workpiece at each weld location the electrodes must be moved open a sufficient distance relative to one another to allow the workpiece to be inserted between them. Typically, the weld controller controls the weld gun to move the electrodes between two extreme states, a fully opened state where the electrodes are spaced apart a maximum distance from one another and a closed state where the electrodes are clamped down on a workpiece. The maximum distance between the electrodes in the fully opened state is typically much greater than the thicknesses of the workpiece at the weld locations. A problem with controlling the weld gun to move the pair of electrodes only between two extreme states is that a considerable amount of time is wasted to move the weld gun between different weld locations.
For instance, after welding a first weld location the weld controller controls the weld gun to open and move the electrodes to the fully opened state. The robot controller then controls the robot arm to move the weld gun to the second weld location to effect welding. Considerable time is wasted between opening the electrodes to the fully opened state after welding the first weld location, moving the weld gun to the second weld location, and then moving the electrodes from the fully opened state to the closed state to clamp down on the workpiece at the second weld location. Specifically, after welding the first weld location the electrodes are opened to a distance much greater than the thickness of the second weld location. This wastes time as the electrodes only need to be moved away from each other at a distance large enough such that the electrodes can clamp down on the workpiece at the second weld location, i.e., a distance large enough such that the workpiece can be inserted between the electrodes at the second weld location.
Prior art weld and robot controllers are also configured to use programmed time delays to ensure that the electrodes are opened a sufficient distance with respect to one another before the weld gun is moved between different weld locations. The prior art weld controllers wait a programmed squeeze cycle delay while the electrodes are closing and moving towards the workpiece to clamp down on the workpiece at a weld location prior to initiating weld power. Electrical power is applied to the electrodes to effect welding at the weld location after the squeeze cycle delay. After the workpiece has been welded at the weld location, the prior art robot controllers wait a programmed open gun cycle delay while the electrodes open and move away from the workpiece at the weld location. The prior art robot controllers then move the weld gun to the next weld location. The problem with using the programmed delays is that the delays are typically conservative to allow enough time for the electrodes to move toward and away from the workpiece prior to initiating weld power at a weld location and prior to moving the weld gun between weld locations.
What is needed is a welding method and system in which a weld controller opens the electrodes of a weld gun just enough after welding a first weld location of a workpiece to clamp the workpiece at a second weld location prior to moving the weld gun from the first weld location to the second weld location.
A further problem with typical weld controllers, and welding operations in general, is that the weld controllers have no backup plan if a weld location is improperly welded. What is needed is a welding method and system in which a weld controller moves the weld gun from a primary weld location to an associated alternative weld location when the workpiece has been improperly welded at the primary weld location.